Methane is a greenhouse gas and, after carbon dioxide, is the second largest driver behind the human-induced increase in climate warming. Methane in the atmosphere has a much shorter lifespan (~12 years) than carbon (~100-300 years), so changes in emissions of methane can have effects within just a few years.

The EPA has developed programs to decrease emissions and this study shows that the effects of these efforts from 1993-2013 are encouraging and reason to expand these programs.

Efforts to reduce emissions include voluntary programs and mandatory regulations, but all focus on the largest methane sources in the U.S.: Oil and natural gas, landfills, coal mining and animal manure management. At the time of publication of this study, the only federal regulations in-place specific to methane emissions for climate were aimed at vehicle emissions.*

From 1993-2013, regulations accounted for ~70% of methane emissions reduction while voluntary programs accounted for ~30%. Total methane emissions reduction over this period was 18%. Without the success of these programs and regulations, global average temperatures today would be 0.006°C higher, with 0.004°C attributed to mandatory regulations and voluntary programs responsible for the remaining 0.002°C. Considering that the global surface temperature over this period increased 0.3°C, this means that U.S. methane regulations and programs reduced global warming by about 2% over this 20-year time-period. This is an enormous contribution from a single nation addressing one specific type of emissions.

The ‘Social Cost of Methane’ refers to the future financial savings derived from reduction of methane emissions now. The monetized health and climate benefits of these reductions over the 1993-2013 period is estimated at $255 billion.

Municipal Solid Waste LandfillsVoluntary programs and regulations for landfills account for 75% of the total methane emissions reduction across all sectors over the 1993-2013 period. The 1996 Landfill Rule accounted for 98% of that reduction. This rule was specific to Non-Methane Organic Compounds mostly over concerns about air quality and health, but had the added benefit of removing methane in the process. Over this 20-year period, methane emissions from the landfill sector decreased 40%.

Oil and Natural GasThe voluntary Natural Gas STAR program accounts for 18% of the total methane emissions reduction across all sectors from 1993-2013, and the NESHAP Rule, requiring controls on all hazardous air pollutants, accounts for 1% of total methane emissions over this period. The success of the Natural Gas STAR program led to its expansion to international partners in 2006. Over this 20-year period, methane emissions from the oil and natural gas industries decreased 14%.

Coal MiningVoluntary programs, principally the Coalbed Methane Outreach Program (CMOP), in the coal mining sector accounts for 5% of total methane emissions reduction across all sectors from 1993-2013. This program focused on the capture and reuse of methane as an energy source in active and abandoned mines. Without CMOP, annual methane emissions would have been 6-14% higher over this 20 year period.

Manure ManagementThe voluntary AgSTAR program accounts for 0.1% of the total methane emissions reduction across all sectors from 1993-2013. However, national methane emissions from the animal manure management sector have increased by 56% over this period. This due to an increase in the use of liquid manure management, especially on pig and dairy cow farms. Without participation in these voluntary reduction programs, annual emissions would have been 1.3% higher in 2013.

*A regulation finalized in November of 2016 requires oil and gas companies to reduce methane emissions on federal and tribal lands. This regulation could be overturned in February of 2017 when the House and Senate can vote to nullify recently finalized federal regulation by a simple majority vote and approval from the president.(For more information, see http://www.sciencemag.org/news/2016/11/trump-and-next-congress-could-quickly-erase-scores-major-regulations)